Wasā’il al-Shīʿa, Chapter on the non-impurification of rain-water in the state of its descent by solely coming in contact with the najasa – Ḥadīth #9

9 – `Ali b. Ja`far in his book from his brother Musa عليه السلام:
He said: I asked him about the rain that flows in the place in which there is excrement, and it contacts the garment, does one pray in it prior to it being washed? He said: When the rain flowed with it, there is no harm.